When an electric plug is pulled from a receptacle under load, energy in the form of inductance in the load and associated wiring may cause an arc between the plug blade and receptacle contact at the tip of the plug blade. In environments where an explosive atmosphere may develop due to the presence of explosive vapors or gasses, such an arc could serve as an ignition source.
Electrical receptacles for preventing inadvertent electric shocks and for arc protection have been proposed. These receptacles have typically employed a mechanically actuated switch to sense the presence of a plug blade in the receptacle. When the plug is inserted into the receptacle to a predetermined position, a plug blade contacts the switch, closing a relay in series with the receptacle contacts to provide power to the receptacle. When the plug is removed from the receptacle, the switch opens as the blade is retracted past the predetermined position, opening the relay to de-energize the receptacle before the plug blade is completely separated from the receptacle contacts. However, these devices have several drawbacks. The energy in the load inductance may cause arcing across the relay contacts. The inductance of the relay coil may also cause an arc across the switch contacts. Thus, a sealed relay and a sealed switch would be required in environments where there is a potential for an explosive atmosphere to develop.
Moreover, mechanical switches and relays also have a relatively slow response time. Testing has demonstrated that in one case a standard three-pronged plug may be removed from a receptacle in as little as six milliseconds. This could occur if the power cord or plug is inadvertently jerked from the receptacle, for example if a person accidentally tripped on the cord, kicked the plug or if the cord is entangled by a piece of moving machinery. If the switch/relay combination does not de-energize the receptacle within this short time, an arc may occur between the plug blade and the receptacle contacts as the plug is removed from the receptacle. Thus, there exists a need for an electrical receptacle with arc protection that is capable of rapidly de-energizing the receptacle in the event that a plug is jerked or rapidly removed from the receptacle without a resulting arc.